Control method for controlling a robot and control system employing such a method

ABSTRACT

A control method for the control of a robot by an operator, using control means which may be positioned at will at different locations of an item to be manipulated, comprises at least a step of determining the position and attitude of the control means on the basis of measurements of forces applied to the control means, defining a first force torsor, and on the basis of corresponding forces, at the gripping member of the robot for example, a step of determining force or force/position control setpoints for the robot on the basis of, at least, measurements of forces on the control means applied to move the item, and of the position and attitude determined during the determination step, and a control step in which the determined setpoints are sent to the robot. A control system employing such a method is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International patent applicationPCT/EP2012/074868, filed on Dec. 7, 2012, which claims priority toforeign French patent application No. FR 1161402, filed on Dec. 9, 2011,the disclosures of which are incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to a control method for controlling arobot and a control system employing such a method. According to thepresent invention, the robot is controlled by a human operator, usingcontrol means. The present invention is applicable, notably, to thecontrol of industrial robots used for moving and positioning heavy andbulky loads.

BACKGROUND

Industrial robots can be used to move an object in space according to acertain number of degrees of freedom of the latter. These robots areused for moving items which are typically too heavy or too bulky to bemoved by a human operator, on production lines for example. These robotscan also provide precise positioning of these items, for the purpose ofassembly operations, for example. Not all the tasks performed byindustrial robots can be entirely automated, and some of them musttherefore be controlled by a human operator. Typically, an industrialrobot is a system comprising a plurality of joints, made after thepattern of a human arm. It may take the form of a manipulator arm,fitted at one end with a gripping member adapted to grasp the item. Theitem may be oriented spatially by the robot, for example by rotationabout three axes, and by translation along the said three axes; in allcases, the combined movements of the components of the robot must allowthe item to be manipulated so as to be moved and oriented in space.

There are various systems for controlling these robots. In a firsttechnique, commonly called “remote operation”, an operator is able tocontrol the robot at a distance, by means of an interaction referred toas indirect. Typically, the robot may be controlled by means of acontrol device which conventionally takes the form of a control boxhaving a plurality of push buttons for initiating various movementactions. The control box can then be used to move the gripping member ofthe robot, pressure on a button being, for example, associated with amovement according to one of the six degrees of freedom, in a givendirection.

A drawback of this technique is that a control box does not allow theoperator to sense the forces applied by the robot and the environment tothe manipulated item, although this data feedback may be essential forthe correct performance of certain tasks such as assembly tasks.

A further drawback of this technique is that it allows the movement ofthe item to be controlled only within frames of reference associatedwith the robot, or more precisely with the robot's gripping member, orwith one of the articulations of the manipulator arm, for example.However, the operator is concerned with the manipulation of the itemitself, rather than with the control of the robot as such: he maytherefore prefer to be able to control the movement of the item indifferent frames of reference, such as those associated with the item.Thus a remote operation technique may be useful for placing the robot ina particular configuration in space, but it is less suitable for theprecise manipulation of an item, the required degree of precision being,for example, greater when it is necessary for the item to be in contactwith its environment.

An alternative known technique, commonly referred to as“computer-assisted remote operation with force feedback” can partiallyovercome the aforesaid drawbacks. According to this technique, thecontrol device is not made in the form of a box fitted with buttons, butrather in the form of a member which may be called a “master arm”, forexample a control lever, or “joystick” as it is called in English, whichcan be moved in space by the operator, and causes the movement of therobot, which is then called a “slave”. The control lever may be providedwith movements controlled by a dedicated controller, allowing theprovision of a force feedback perceptible to the user. One advantage ofthis technique is that it allows more intuitive control of the robot.Furthermore, the fact that this technique allows the operator to sensethe forces applied to the robot helps to provide more precise assistanceto the latter, notably during the performance of tasks in which themanipulated item comes into contact with external elements. According tothis technique, the operator is able to choose frames of reference inwhich the robot is to be controlled to perform specific tasks; indeed,the operator may even be able to specify the tasks to be performed bythe robot.

A drawback of this technique is that it requires the operator to specifythe frames of reference or the tasks, for example if he wishes tomanipulate the item in frames of reference other than those of therobot, which may prove to be difficult and, in particular, impracticalduring the manipulation of an item.

A further drawback of the two aforesaid techniques relates to theoperator's viewpoint of the scene, in that the operator has to remain ata specific location, and is not free to choose his viewpoint of thescene, unless he uses video camera systems, for example; that is to say,unless he accepts additional constraints in terms of the number ofsensors used, as well as constraints relating to the positioning ofthese sensors, notably for the purpose of avoiding possible obscuration.

It may thus be preferable for the operator to remain in the proximity ofthe scene. There are known control systems by means of which theoperator can interact directly with the robot, for example by using acontrol handle fixed to the gripping member of the robot, and enablingthe operator to cause the movement of this member. In this way, the itemcan be manipulated with its six degrees of freedom, with the provisionof exact compensation for the weight of the item. However, moreespecially if the operator has to manipulate a large item in a precisemanner, he may find it difficult to control the robot simply by means ofa control handle fixed to one end of the robot's arm. It may beessential for the operator to grasp a particular location on the item inorder to manipulate it in a certain way; moreover, the handle fixed onthe robot may move out of the operator's reach when the robot has tograsp a large item on its own.

In order to overcome these drawbacks, control systems have been designedwhich enable an operator to interact with an item to be manipulated bymeans of the item itself, by using a control member, separate from therobot and allowing direct interaction with the item, located at one endof the item. A control system of this type is described in the Japanesepatent application published under the reference JP 2008/213119. In thiscontrol system, a handle separate from the robot may be positioned at apredetermined location on a frame supporting the item to be manipulated.

A drawback of this control system arises from the fact that the item canbe controlled only in the frame of reference of the robot or of thehandle, which is fixed with respect to the control system, making itnecessary for the orientation and position of the frame of reference ofthe handle with respect to the robot to be predetermined and knownduring the implementation and adjustment of the robot control, and toremain fixed subsequently.

Furthermore, the grasping position may not always be suitable for themanipulation of the item: for example, if the item has to be turnedover, the handle may be located under the item when the latter has beenturned over, causing difficulties in manipulation. The grasping positionmay also prove to be unsuitable if, for example, the item has to beassembled with another item, as the handle may obstruct the assemblyoperation in some configurations.

A further drawback of systems in which the forces applied by the humanoperator are applied remotely from the robot is due to the fact that theforces applied by the operator at the point where he grasps the item aredifferent from the forces experienced by the gripping member of therobot, possibly giving rise to ambiguities between different movements,for example rotational and translational movements. For example, in aconfiguration in which the operator and the gripping member of the robotgrasp each end of an item, for example a plank, the force experienced bythe gripping member of the robot resembles a torque, regardless ofwhether the operator wishes to make the item pivot about the robot'seffector or to translate it.

SUMMARY OF THE INVENTION

One object of the present invention is at least to mitigate theaforesaid drawbacks, by proposing a control method and system for arobot enabling an operator to manipulate an item in an intuitive andprecise manner, according to the six degrees of freedom of the item, bya direct physical interaction with the item, while the operator remainscapable of manipulating the item easily, regardless of itsconfiguration.

An advantage of the invention is that a control method or systemaccording to one of the described embodiments enables the force orforce/position control of the robot to be adapted according to itsenvironment and the control by the operator, the latter being free tochoose the frame of reference of manipulation in real time, in anintuitive manner, and being able to interact physically with the item,the robot and the environment at the same time.

A further advantage of the invention is that a control method or systemaccording to one of the described embodiments allows simple manipulationwhich requires no operator training.

A further advantage of the invention is that a control method or systemaccording to one of the described embodiments may be developed from anexisting robot control system, by the addition of a small number ofinexpensive, compact devices.

A further advantage of the invention is that a control method or systemaccording to one of the described embodiments makes it possible toresolve possible ambiguities between translational and rotationalmovements.

A further advantage of the invention is that a control method or systemaccording to one of the described embodiments makes it possible to usevirtual guides determined as a function of the forces applied by theoperator on the control means and the position of these control means,thus providing additional assistance to the operator.

A further advantage of the invention is that a control method or systemaccording to one of the described embodiments is robust against possibleobscuration and against possible variations in illumination, andrequires no preliminary positioning of sensors. Obscuration andvariations of illumination may, notably, adversely affect the operationof control systems using handle location means based on optical sensorssuch as cameras, or on acoustic sensors, the latter being, for example,equally sensitive to obscuration. A control system according to one ofthe described embodiments is also robust against parasitic magneticfields and objects with high magnetic permeability present in theenvironment, and may adversely affect the operation of the controlsystems using handle location means based on magnetic field sensors.

A control system according to one of the described embodiments is alsorobust against walls which are present in the environment, and which mayadversely affect the operation of control systems using radio frequencyhandle location means, which are affected by the “multipath” problem dueto the multiple paths of reflected radio waves.

A control system according to one of the described embodiments is alsorobust against the drift of the position and orientation to bedetermined that may occur in control systems using handle location meansbased on inertial sensors and the integration of their measurements.

For this purpose, the invention proposes, in a first embodiment, acontrol method for a robot comprising at least one articulation and atleast one gripping member adapted to move an item in space, the robotbeing controlled by control means, the method comprising a concatenationof at least the following steps:

-   -   a step of positioning control means on the item,    -   a step of determining the position and attitude of the control        means on the basis of measurements of forces applied to the        control means, defining a first force torsor, and corresponding        forces at the gripping member of the robot, defining a second        force torsor,    -   a step of determining force or force/position control setpoints        on the basis of measurements of forces on the control means        applied to move the item, and of the position and attitude        determined during the determination step,    -   a control step in which the determined setpoints are sent to the        robot.

In a second embodiment of the invention, the position and attitude ofthe control means can be determined by minimizing the error between themeasurement of one of two torsors chosen from said first force torsorand said second force torsor, and the measurement of the same torsorreconstructed from the measurement of the other of these two torsors,using Varignon's relation.

In a third embodiment of the invention, the position and attitude of thecontrol means can be determined by on-line processing of the forcetorsors obtained from the force measurements, using a recursivealgorithm.

In a fourth embodiment of the invention, said recursive algorithm may bean unscented Kalman filter.

In a fifth embodiment of the invention, the position and attitude of thecontrol means can be determined by off-line processing of the forcetorsors obtained from the force measurements, based on a recording ofthe corresponding data over a specified period, using an optimizationalgorithm.

In a sixth embodiment of the invention, said optimization algorithm maybe based on the Nelder-Mead method.

In a seventh embodiment of the invention, the control method may furthercomprise a step of checking the fixing of the control means to theitems, which is performed after the positioning step.

In an eighth embodiment of the invention, the control method may furthercomprise a location checking step in which the consistency of thedetermined position and attitude of the control means is determined bycomparing a confidence level, associated with the estimated valuesdetermined by the recursive algorithm, with a predetermined level.

In a ninth embodiment of the invention, the control method may furthercomprise a location checking step in which the consistency of thedetermined position and attitude of the control means is determined bycomparing a confidence level, associated with the estimated valuesdetermined by the off-line processing, with a predetermined level.

In a tenth embodiment of the invention, the control method may furthercomprise a location checking step in which the consistency of thedetermined position and attitude of the control means is determined bycomparing the position and attitude determined in the determination stepof the control means with a position and attitude of the control meansdetermined according to an estimation or identification algorithm on thebasis of at least measurements of acceleration and orientation orangular velocity of the control means (100) made by means of appropriatesensors.

In an eleventh embodiment of the invention, the step of setpointdetermination may be replaced by a substitute determination step inwhich the control setpoints of the robot are determined solely on thebasis of the force and/or position measurements made at the grippingmember of the robot, or at said at least one articulation of the robot,if the fixing of the control means to the item is inappropriate.

In a twelfth embodiment of the invention, the step of setpointdetermination may be replaced by a substitute determination step inwhich the control setpoints of the robot are determined solely on thebasis of the force and/or position measurements made at the grippingmember of the robot, if the determined position or attitude of thecontrol means is inconsistent.

The present invention also proposes a control system for a robotcomprising at least one articulation and a gripping member adapted tomove an item in space, the control system comprising:

-   -   means for measuring forces applied at the gripping member of the        robot,    -   control means adapted to be fixed to the item and comprising        means for measuring forces applied to the control means,    -   collection means configured to collect the force measurements        made by the means for measuring forces applied at the gripping        member of the robot and to the control means,    -   a controller configured to employ the collection means,

the controller being further configured to employ a control methodaccording to the aforementioned first embodiment.

In one embodiment of the invention, the control means may comprisereversible fixing means.

In one embodiment of the invention, the control system may furthercomprise means of monitoring the control means, configured to detect thedetachment of the control means from the item, the controller beingconfigured to employ a control method according to the aforementionedseventh embodiment.

In one embodiment of the invention, the control means may be formed byat least one handle comprising a support and a handgrip, the supportbeing designed to be fixed to the item by the fixing means.

In one embodiment of the invention, the control means may be formed byat least one glove.

The present invention proposes to determine the torsor of forces appliedby the operator to the control means in a frame of reference associatedwith the robot, for the purpose of controlling the latter. The controlmethod or system according to the present invention also makes itpossible to determine precisely the position and attitude of the controlmeans, in the form of one or more handles for example, these data beingused in order to exploit the force measurements of the control means forthe purpose of determining the control setpoints of the robot. Thehandle or handles can thus be positioned as desired on the item to bemanipulated, and can be fixed to it by suitable fixing means, thesemeans being reversible, that is to say allowing an operator to removethe handle or handles easily from the item so that they can bepositioned at another location on the item if required.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will become clearin the light of the description provided by way of example, withreference to the attached drawings which represent:

in FIG. 1, a profile view illustrating a control system according to anembodiment of the present invention;

in FIG. 2, a sectional view illustrating in a synoptic way the structureof a handle forming a control means according to an embodiment of theinvention;

in FIG. 3, a flow chart showing a control method for a robot, accordingto one embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a robot 1, comprising for example a manipulator arm 11 atthe end of which is placed a force sensor, not shown in the figure,operating for example with six axes of freedom, in which case the sensoris called a “six-axis sensor”. A gripping member 13 is positioned in theterminal part of the manipulator arm 11. The gripping member 13 graspsan item 15 to be manipulated. Control means, formed by a handle 100 inthe example illustrated in the figure, may be fixed to the item 15. Thehandle 100 can be grasped by an operator, not shown in the figure, andmay be positioned at a desired location on the item 15 as the operatorwishes.

An example of a structure of the handle 100 is described below withreference to FIG. 2. The handle 100 may notably comprise fixing meansfor fixing to the item, so that it is held in place despite the forcesexerted on it during the manipulation of the item 15, that is to sayduring the control of the robot 1, and can easily be removed so as to bepositioned at another location. Examples of fixing means are explainedbelow with reference to FIG. 2.

In the example illustrated in the figure, the item 15 to be manipulatedis essentially flat in shape, resembling a plank, but it is to beunderstood that the present invention can be used for the manipulationof different and even complex shapes.

When he has grasped the handle 100, the operator may, for example, usethe handle 100 to impart displacement movements to the item 15 as if hewere applying them directly to the item, the function of the robottypically being to eliminate the operator's perception of the weight ofthe item. The operator may position the handle 100 at the mostadvantageous location on the surface of the item 15 to be manipulated.

Each movement of the handle 100 may require a preliminary phase inwhich, for example, the operator has to exert forces in differentdirections. An off-line estimation or identification algorithm, forexample, may then be used to determine the position and orientation ofthe handle 100, or of the plurality of handles. These principles aredescribed in detail below with reference to FIG. 3.

A controller 110 can deliver control setpoints to the robot 1, and canemploy control algorithms based on input data obtained, notably, fromthe sensors included in the control means and in the robot 1, asexplained below. More generally, the controller 110 can employ a controlmethod according to one of the embodiments of the invention.

A control system according to the present invention may also comprisemeans for collecting the data outlined above, obtained from the sensors,these collection means possibly being included in the controller 110,for example.

The control system may comprise different sensors adapted to collectmeasurements of the forces applied at the gripping member of the robot.These sensors are usually added to irreversible or low-reversibilityrobots which are widely represented in the range of industrial robots,and which are made to evolve and be in contact with their environment,including the operator.

It should be noted that the force sensor may, for example, be amulti-axis sensor located on the gripping member of the robot. It isalso possible to position sensors, for example torque sensors, at thearticulations of the robot; the measurements made by these sensors canthen enable force measurements to be made at the gripping member of therobot. Force measurements may also be obtained from measurements of thecurrent supplied to the motors of the robot's articulations.

According to a specific feature of the present invention, the controlmeans, that is to say the handle 100 in the example illustrated in thefigure, comprise means for making measurements of forces applied to thecontrol means. Exemplary embodiments of a handle 100 provided with thesemeans are described below with reference to FIG. 2.

With reference to FIG. 2, a handle 100 may comprise a graspable element101 that can be grasped by an operator's hand, and a support 103. Thehandle 100 also comprises a force sensor 105 for capturing the forcesalong the six axes, and for returning force signals representative ofthese forces. The base of the support 103 may comprise fixing means 109.

The fixing means 109 must be such that the fixing of the handle 100 tothe item to be manipulated is sufficiently robust to the movementsimparted by the operator, while still allowing the operator to removethe handle 100 easily in order to position it, at his discretion, atanother location on the item. The fixing means 109 can therefore bedescribed as “reversible”.

For example, the fixing means 109 may take the form of self-grippingstrips, the surface of the item being possibly treated to allow thefixing of these strips.

If the item to be manipulated is made of a ferromagnetic material, thefixing means 109 may take the form of a permanent magnet or anelectromagnet.

The fixing means 109 may also take the form of a suction pad, or asuction system operated by a pump.

The fixing means 109 may also take the form of an adhesive strip.

In the exemplary embodiment shown in FIG. 2, the force sensor 105 ispositioned in the support 103 and is a six-axis force sensor.

Advantageously, the handle 100 may comprise additional measuring means107.

The additional measuring means 107 may, for example, comprise at least a3D accelerometer and/or one or more 3D rate gyroscopes. The additionalmeasuring means 107 may, for example, take the form of an inertialguidance unit. At least one 3D accelerometer may, for example, be usedto determine the acceleration due to the Earth's gravity when the handleis in a stationary position, as this information may improve thedetermination of the orientation of the handle. The additional measuringmeans 107 may also make it possible, with the aid of calculation means,for example those using a filter such as a Kalman filter, to estimatethe position and attitude of the handle 100, for example in order toconfirm the determination carried out by the estimation oridentification algorithm described below, or in order to define anappropriate initialization point of the estimation or identificationalgorithm so that the latter converges more rapidly, as described indetail below.

In practice, the operator may grasp one handle or two handles such asthe handle 100 by their graspable elements 101, and may position thehandle or handles 100 wherever he wishes on the surface of the item tobe manipulated. The force sensor 105 can then be used to measure theforces applied by the operator to the handles 100. A force torsor canthen be determined, in the frame of reference of the handle 100. Theforce torsor may be determined in a dedicated calculation module, forexample one implemented in the controller 110, described previously withreference to FIG. 1.

It is then necessary to know the position and the orientation, orattitude, of the handle 100 in order to make use of the aforesaid forcetorsor in the determination of the control setpoints of the robot.

According to a specific feature of the present invention, it is proposedto determine the position and attitude of the handle 100 on the basis ofthe relation between the reduced force torsors at the handle 100 and atthe effector of the robot. This is because, according to the hypothesesof solid mechanics, the relation between the reduced force torsors atthe handle 100 and at the effector of the robot depends solely on therelative position of their respective reduction centers and therespective orientations of their own frames of reference.

This relation, corresponding to Varignon's relation applied to the forcetorsors, can be formulated by means of the following relations:^(r) m _(r)=^(r) m _(o) +RP× ^(r) f= ^(r) R _(p) ^(p) m _(p) +RP×(^(r) R_(p) ^(p) f _(p))=q ^(r) m _(p) q ⁻¹ +RP×(q ^(p) f _(p) q ⁻¹)^(r) f_(r)=^(r) f _(p)=^(r) R _(p) ^(p) f _(p) =q ^(p) f _(p) q ⁻¹  (1),

in which ^(y)X_(z) denotes a variable X expressed in a frame ofreference y in a reduction point z, the force torsor being

$\begin{bmatrix}f \\m\end{bmatrix},$where f is the force vector in three dimensions, and m is the momentvector in three dimensions, while r denotes the effector of the robotand p denotes the handle, RP denotes the vector describing the positionof the handle relative to the effector of the robot in the frame ofreference of the robot, R and q denote, respectively, the rotationmatrix and the quaternion representing the orientation of the handlerelative to the effector of the robot.

In the exemplary embodiment described above, the force torsor at thegripping member of the robot can be determined by means of the six-axisforce sensor.

It is also possible to determine the force torsor at the handle 100, onthe basis of the data collected by the force sensor 105, which can alsobe transmitted by appropriate means to the collecting means of thecontroller 110.

In the exemplary embodiment described above, the operator applies forcesto the handle in given directions in a preliminary phase, to enable theposition and attitude of the handle to be determined, as outlined above.The forces to be applied by the operator in the preliminary phase may,for example, be related to the forces that he would apply if he wantedto ensure that the handle was correctly fixed.

The controller 110 may also be configured to employ a control method forthe robot as described below.

An example of a control method for the robot is described below withreference to FIG. 3.

In a positioning step 301, the human operator positions the handle at agiven location on the item to be manipulated. The positioning step 301may advantageously be followed by a step 302 of checking the fixingmeans, in which a check may be performed as to whether the handle isappropriately fixed. Monitoring means 3020 of the control means maydeliver data representative of the correct fixing of the handle.Examples of monitoring means 3020 are described below. If it is found inthe checking step 302 that the control means are not fixedappropriately, the control system may, for example, be put into what isknown as “degraded” mode 3021, in which the control setpoints of therobot are determined solely on the basis of the data delivered by thesensors present on the robot. Alternatively, if it is found in thechecking step 302 that the control means are not fixed appropriately,the control system may, for example, be put into a safe mode in whichall the degrees of freedom of the robot are blocked.

The checking step 302, or the positioning step 301 if no checking stepis provided, is followed by a step 303 in which the position andattitude of the control means are determined.

An estimation or identification algorithm may be employed during thedetermination step 303, enabling the position and orientation of thecontrol means to be determined relative to the effector of the robot.

First of all, the position and orientation or attitude are initialized.The initial position and attitude may be chosen at will; for example,they may be chosen to be identical to the position and attitude of theeffector of the robot when the control means are fixed for the firsttime to the item to be manipulated. Subsequently, whenever the controlmeans are moved by the operator, the initialization can be carried outon the basis of the position and attitude of the control means estimatedat the end of the preceding movement of these means.

Advantageously, the initialization can be carried out more finely, forexample if additional means such as a 3D accelerometer or an inertialguidance unit in the control means are available. As described above,the initialization may, for example, be carried out on the basis of theprevious knowledge of the acceleration due to the Earth's gravity if anaccelerometer is available, and/or on the basis of an estimate ofposition and/or attitude obtained on the basis of the data of theinertial guidance unit and the use of an estimation filter, if theseelements are available.

The estimation of the position and attitude of the control meansrequires a plurality of measurements of the forces applied at thecontrol means, and of the corresponding forces applied at the effectorof the robot. For this purpose, the operator applies various forces tothe control means, for example forces similar to those which he wouldapply to these means to ensure that they were correctly fixed, asdescribed above.

According to the hypotheses of solid mechanics, it is possible to useVarignon's relation, which can express the torsor applied at a point Aof a solid at another point B of this solid solely by means of theposition and orientation relating these two points, to the reducedtorsors at the effector of the robot, in other words its grippingmember, and at the control means.

According to the present invention, the position and attitude of thecontrol means can be estimated by minimizing the error, or the square ofthe error:

-   -   between the measurement of one of two torsors chosen from a        first torsor formed by the reduced force torsor at the control        means and a second force torsor formed by the reduced force        torsor at the gripping member of the robot, and    -   the same torsor reconstructed from the measurement of the other        of the aforesaid two torsors, using Varignon's relation.

The position and attitude between the control means and the effector ofthe robot are then determined when the error is minimal. The determinedposition and attitude correspond to the pair of their values yieldingthe smallest error.

In practice, the position and attitude of the control means can beestimated by on-line processing and exploitation of the data, using arecursive algorithm, in which the estimation of the current state vectorrequires a knowledge of the preceding state and the presentmeasurements. For example, a Kalman filter may be used. Morespecifically, a Kalman filter of the unscented type, commonly referredto according to the English terminology as an “unscented Kalman filter”or by the corresponding abbreviation “UKF”, may be used.

Alternatively, the position and attitude of the control means can beestimated by off-line processing of the data, by recording all the dataover a specified period and then using an optimization algorithm, usingthe Nelder-Mead method for example.

These algorithms are mentioned by way of example, but it is to beunderstood that other estimation or identification algorithms may beused.

It should be noted that positions and attitudes of a plurality ofdevices are determined if the control means are formed by two handles orother devices described below.

When the position and attitude of the control means have been determinedat the end of the determination step 303, a step 305 of determining thecontrol setpoints of the robot can be performed. The positions andattitudes that are determined enable force or force/position control ofthe robot to be provided on the basis of, at least, measurements offorces at the control means.

Advantageously, a location checking step 304 may be performed after thedetermination step 303 and before the setpoint determination step 305.For example, if additional means 3040 such as a 3D accelerometer or aninertial guidance unit are included in the control means, a consistencycheck can be performed between the estimates provided by theseadditional means. If it is found in the checking step 304 that thedetermined position and/or attitude of the control means areinconsistent, the control system may, for example, be put into what isknown as a “degraded” mode, and the position and attitude may then bedetermined in a substitute determination step 3021, in which the controlsetpoints of the robot are determined solely on the basis of the datadelivered by the sensors present on the robot. Alternatively, if it isfound in the location checking step 304 that the determined position andattitude of the control means are inconsistent, the control system may,for example, be put into a safe mode in which all the degrees of freedomare blocked, or in which only the degrees of freedom corresponding tothose for which the additional means allow the diagnosis of aninconsistency are blocked. It is possible to proceed in a parallel waywith the determination of the position and attitude of the handle,according to the determination step 303, until the position and attitudeare considered to be consistent. It is also possible for the fixingmeans to be checked in advance according to the checking step 302.

If these additional means are not used, a consistency check may also beperformed in the location checking step 304, by an assessment of theconfidence level associated with the estimated values. If thisconfidence level is beyond a specified threshold, the control system maybe put into the degraded mode or into a safe mode in which all thedegrees of freedom of the robot are blocked.

The setpoint determination step 305 is followed by a control step 307 inwhich the setpoints are sent to the robot.

To summarize, as soon as the location of the control means isconsistent, the forces applied to the control means are determined, andthe robot is controlled at least on the basis of these forces. All thesesteps form a loop and are repeated, for example, until it is detectedthat the control means are no longer fixed, or that the location is nolonger considered to be consistent, if means are provided for thispurpose. The method can then be resumed according to the flow chartshown in FIG. 3.

Advantageously, it is possible to determine the position and attitude ofthe control means by applying the aforesaid Varignon's relation and itsderivative, respectively, to the angular velocities and to theaccelerations measured by the inertial guidance unit and by sensors ofacceleration and angular velocity placed on the robot, thelast-mentioned data also being obtainable from data on the position ofthe robot supplied by position sensors placed on the robot. The positionand attitude of the control means can then be estimated according to thepreviously described principle applied to the force torsors, in otherwords by minimizing the error, or the square of the error:

-   -   between the measurement of one of two composite acceleration and        angular velocity vectors chosen from a first vector formed by        the vector expressed at the control means and a second vector        formed by the vector expressed at the gripping member of the        robot, and    -   the same vector reconstructed from the measurement of the other        of the aforesaid two vectors, using Varignon's relation and its        derivative.        Similarly, the error may also be minimized by using means        similar to the means described above in relation to the force        torsors.

According to this advantageous embodiment, the inertial guidance unit isused according to a method which has the advantage of requiring nointegration of measurements, and which therefore does not cause drift.

The estimation algorithm and the various aforesaid steps may be employedin the controller 110 or by dedicated means.

Advantageously, the torsor of forces applied to the control means may beused to detect an intention of the operator, and to activate a commandto the robot as a function of this intention, so as to constrain thetrajectory of the robot. For example, an intention to perform atranslational movement may be detected, and the robot may then becommanded to perform a translation, without taking into account anyinvoluntary movements of the operator which might divert the item fromits translational movement. Thus the item is moved according to virtualguides. The principle of virtual guides is permitted by a method or asystem according to the present invention, and enables supplementaryassistance to be given to the operator's gesture, the operator beingable to specify on-line the use of this assistance, as a result of thepositioning of the control means and the forces applied to them. Thechoice of the virtual guide may be determined as a function of thedirections and senses of the forces applied by the operator to thehandle, the combination of these forces, and the position in which theyare applied. For example, if the operator wishes the item to rotateabout the handle, he will apply only a torque about the axis about whichhe wishes to make the item rotate, and all the other forces will bezero. In this case, it is possible to determine that the robot mustdescribe a circle about the axis of the applied torque, with theposition of the handle at its center, the sense—or sign—of the torquegiving the direction in which the circle is to be described by therobot. If virtual guides are used, the robot may be controlled byforce/position control.

With reference once again to FIG. 2, and as mentioned previously withreference to FIG. 3, the handle 100 may advantageously comprise means ofmonitoring the control means, configured to detect the detachment of thehandle 100 from the item. The means of monitoring the control means may,for example, take the form of a movable appendage mounted on a springand positioned in the center of the base of the support 103, that is tosay at the fixing means 109. The means of monitoring the control meansmay also simply take the form of the determination of the position ofthe handle: if the position of the handle 100 is determined to be at adistance greater than a specified threshold value, it may be concludedthat the handle has not been kept fixed, and has slipped, for example.

Advantageously, the control means may take the form of a glove or a pairof gloves, in order to facilitate the manipulation even more for theoperator.

A glove may, for example, comprise a plurality of pressure sensors, andadvantageously at least one additional sensor for determining theorientation of the hand.

Also advantageously, the glove may further comprise multi-axis forcesensors.

The invention claimed is:
 1. A control method for a robot comprising atleast one articulation and at least one gripping member adapted to movean item in space, the robot being controlled by control means, saidmethod comprising a concatenation of at least the following steps: astep of positioning control means on the item, a step of determining theposition and attitude of the control means on the basis of measurementsof forces applied to the control means, defining a first force torsor,and corresponding forces at the gripping member of the robot, defining asecond force torsor, a step of determining force or force/positioncontrol setpoints for the robot on the basis of measurements of forceson the control means applied to move the item, and of the position andattitude determined during the determination step, a control step inwhich the determined setpoints are sent to the robot.
 2. The controlmethod of claim 1, wherein the position and attitude of the controlmeans are determined by minimizing the error between the measurement ofone of two torsors chosen from said first force torsor and said secondforce torsor, and the measurement of the same torsor reconstructed fromthe measurement of the other of these two torsors, using Varignon'srelation.
 3. The control method of claim 2, wherein the position andattitude of the control means are determined by on-line processing ofthe force torsors obtained from the force measurements, using arecursive algorithm.
 4. The control method of claim 3, wherein saidrecursive algorithm is an unscented Kalman filter.
 5. The control methodof claim 2, wherein the position and attitude of the control means aredetermined by off-line processing of the force torsors obtained from theforce measurements, on the basis of a recording of the correspondingdata over a specified period, using an optimization algorithm.
 6. Thecontrol method of claim 5, wherein said optimization algorithm is basedon the Nelder-Mead method.
 7. The control method of claim 1, furthercomprising a step of checking the fixing of the control means to theitem, which is performed after the positioning step.
 8. The controlmethod of claim 3, further comprising a location checking step whichdetermines the consistency of the determined position and attitude ofthe control means by comparing a confidence level, associated with theestimated values determined by the recursive algorithm, with apredetermined level.
 9. The control method of claim 5, furthercomprising a location checking step in which the consistency of thedetermined position and attitude of the control means is determined bycomparing a confidence level, associated with the estimated valuesdetermined by the off-line processing, with a predetermined level. 10.The control method of claim 3, further comprising a location checkingstep in which the consistency of the determined position and attitude ofthe control means is determined by comparing the position and attitudedetermined in the determination step of the control means with aposition and attitude of the control means determined according to anestimation or identification algorithm on the basis of at leastmeasurements of acceleration and orientation or angular velocity of thecontrol means made by means of appropriate sensors.
 11. The controlmethod of claim 7, wherein the step of setpoint determination isreplaced by a substitute determination step in which the controlsetpoints of the robot are determined solely on the basis of the forceand/or position measurements made at the gripping member of the robot,or at said at least one articulation of the robot, if the fixing of thecontrol means the item is inappropriate.
 12. The control method of claim8, wherein the step of setpoint determination is replaced by asubstitute determination step in which the control setpoints of therobot are determined solely on the basis of the force and/or positionmeasurements made at the gripping member of the robot, if the determinedposition or attitude of the control means is inconsistent.
 13. A controlsystem for a robot comprising at least one articulation and a grippingmember adapted to move an item in space, the control system comprising:means for measuring forces applied at the gripping member of the robot,control means adapted to be fixed to the item and comprising means formeasuring forces applied to the control means, collection meansconfigured to collect the force measurements made by the means formeasuring forces applied at the gripping member of the robot and to thecontrol means, a controller configured to employ the collection means,the control system being characterized in that the controller is furtherconfigured to employ a control method as claimed in claim
 1. 14. Thecontrol system of claim 13, wherein the control means comprisereversible fixing means.
 15. The control system of claim 13, furthercomprising means for monitoring the control means, configured to detectthe detachment of the control means from the item, the controller beingconfigured to employ a control method according to claim
 7. 16. Thecontrol system of claim 13, wherein the control means are formed by atleast one handle comprising a support and a handgrip, the support beingdesigned to be fixed to the item by the fixing means.
 17. The controlsystem of claim 13, wherein the control means are formed by at least oneglove.